Apparatus for grinding drills



1970 E. BORCHERT m, ETAL 3,543,445

APPARATUS FOR GRINDING DRILLS 8 Sheets-Sheet 1 Filed April 14, 1967 INVENTOR 55M 7- flue GAIL-'87 E BY day/v easier $00744 4N0 Dec. 1, 1970 E. BORCHERT m, ETAL 3,543,445

APPARATUS FOR GRINDING DRILLS Filed April 14, 1967 8 Sheets-Sheet 2 JVENTORS Ee/wr Ease/men? BA/Av 01m? ean/14w Dec. 1, 1970 E. BDRCHERT m, ETAL. 3,5 5

I APPARATUS FOR GRINDING DRILLS 8 Sheets-Sheet S Filed April 14 INVENTOR. [ax/5r Beam/Ezra c/bwv @oezeffaamzwp 9.1

4rrlves Dec. 1, 1979 E. BORCHERT m, ETAL 3,543,445

APPARATUS FOR GRINDING DRILLS Filed April 14, 1967 8 Sheets-Sheet -L I 1, 1970 E. BORCHERT m, ETAL. I 35 APPARATUS FOR GRINDING DRILLS Filed April 14, 1967 8 Sheets-Sheet 5 Dem 1970 E. BORCHERT ETAL 3,543,445

APPARATUS FOR GRINDING DRILLS Filed April 14, 1967 s Sheets-Sheet e Nara/4w: INVENTOR,

r Base/ seri JE 05.52; .sbl/f/lM fig? Dec. 1, 1970 E. BORCHERT m, ETAL 3,543,445

' APPARATUS FOR GRINDING DRILLS Filed April 14, 1967 8 Sheets-Sheet 7 E. BORCHERT m, ETAL 3,543,445

APPARATUS FOR GRINDING DRTLLS [1957 s Sheets-Sheet e Dec. 1, 1970 Filed Abril 14 United States Patent 3,543,445 APPARATUS FOR GRINDING DRILLS Ernst Borchert III, Pomona, and John Robert Southland,

Arcadia, Califi, assiguors to Winslow Product Engineering Corporation, Arcadia, Calit., a corporation of California Filed Apr. 14, 1967, Ser. No. 630,885 Int. Cl. B24b 7/02 US. Cl. 51-33 20 Claims ABSTRACT OF THE DISCLOSURE Precision grinding apparatus for splitting the point of a twist drill to produce secondary cutting edges, thereby improving the drilling efliciency and accuracy of the drill, especially in harder metals. A grinding wheel sweeps progressively across a drill oriented in a drill holder that automatically rotates the drill 180 to grind both flutes equally and evenly using a grinding wheel having a frusto-conical grinding surface.

BACKGROUND OF THE INVENTION The field of the present invention is, broadly, grinding apparatus; but more especially the invention is concerned with apparatus for grinding the cutting end of a twist drill to improve drilling efliciency and accuracy. The invention is referred to in a broad sense as grinding apparatus; but it does not accomplish or replace the familiar pointing or sharpening operation that provides the primary cutting edges of the drill. Rather it performs an added grinding operation whereby additional cutting edges are produced on the end of the drill near the center.

The most commonly followed procedure in pointing a drill is to grind a conical surface on the end of the drill. On a twist drill with two flutes, the two surfaces produced by such drill pointing, one on each flute, intersect at a short ridge crossing the central axis of the drill. With this shape, the drill has a tendency to ride on this ridge and not cut well since the ridge scrapes the work rather than out a free chip.

While various other surface shapes have been devised, it has been discovered that the ridge can be eliminated with attendant increase in efliciency and accuracy of the drill by removing more metal at the heel of each flute after the regular sharpening operation. The result is a short secondary cutting edge extending radially outwardly from the axis at two opposite sides thereof at the location of the former ridge. The drill now has a point on the drill axis and cutting edges now cut over the full area of the hole being drilled.

It is basic to all drilling operations that for accuracy, both as to straightness of the hole and uniformity of diameter, the drill must be precisely symmetrical about its longitudinal axis. In other words, ground surfaces must be symmetrical in all respects. Even if the flutes are not shaped symmetrically, an accurate hole is produced if the grinding at the cutting end is precise and symmetrical about the axis of rotation.

In apparatus of this character, it is accordingly a general object of the invention to provide means producing a high degree of precision in grinding surfaces that are truly symmetrical about the axis of rotation of the drill.

It is also an object to provide novel means for holding and orienting a drill during grinding operations and that automatically grind the drill equally at two positions spaced 180 apart.

A further object is to grind the drill progressively across its face in order to reduce the tendency to overheat the drill.

SUMMARY OF THE INVENTION The apparatus of the present invention comprises a frame, a drill holder adjustably mounted on the frame for holding a drill in a predetermined position, a rotatably mounted grinding wheel mounted on the frame to traverse a given path, means for rotating the grinding wheel, and means causing the grinding wheel to traverse said path which brings it into contact with the end of the drill. The several movements can conveniently be controlled in timed relation to each other by an electromechanical control system.

The drill holder for holding the drill is mounted on the frame in a manner to be adjustably positioned in several aspects; but the drill is held stationary during the grinding operation. The drill holder includes a locator engaging the end of the drill which establishes the position of the drill both longitudinally and angularly with respect to the drill axis prior to grinding. The grinding wheel has two peripheral surfaces of frusto-conical shape which intersect at the maximum diameter of the wheel. This maximum diameter engages the drill at substantially the axis of the drill with the upper One of the frusto-conical surfaces the major grinding surface. The grinding wheel sweeps forwardly and returns over a given path during which the wheel contacts the drill to shape it; and between two successive traverses, each consisting with forward and return stroke, the drill is automatically rotated in the drill holder so that the drill is accurately ground equally at two positions.

Because the grinding faces on the wheel become worn, means are provided to restore them to the desired shape, such means being in the form of a dresser which shapes both frusto-conical faces on the wheel simultaneously. One purpose of this dresser is to retain the maximum diameter of the grinding wheel at a predetermined posi tion with respect to the drill.

DESCRIPTION OF THE DRAWINGS How the above and other objects and advantages of the present invention are attained will be more readily understood by reference to the following description and to the annexed drawing, in which:

FIG. 1 is a front, side and top perspective of the completed grinding apparatus enclosed in a cabinet of which the lid is lifted and a portion broken away.

FIG. 2 is a plan view of the top of the machine with the lid of the cabinet removed.

FIG. 2a is an end view of the wheel dresser assembly viewed in the direction of the arrow 2a in FIG. 2.

FIG. 2b is a fragmentary plan view of a portion of FIG. 2;

FIG. 3 is a fragmentary vertical section on line 3-3 of FIG. 2.

FIG. 8 is a side elevation of the drill holder viewed in the direction of arrow 8 in FIG. 2.

FIG. 8a is a fragmentary horizontal section through the base of the drill holder taken on line 8a8a in FIG. 8.

FIG. 9 is a longitudinal median sectional view of the drill holder, portions of the outer housing being broken away.

FIG. 9a is an elevation of the locator head taken on line 9a9a of FIG. 9.

FIG. is an end elevation of the drill holder when viewed in the direction of arrow 10 in FIG. 9.

FIG. 11 is a transverse section through the drill holder on line 1111 in FIG. 9.

FIG. 12 is a fragmentary elevation taken on line 12-12 of FIG. 10 with part broken away.

FIG. 13 is a diagrammatic view of the grinding wheel and the mounting means therefor, showing the components of the movement of the grinding wheel.

FIG. 14 is a fragmentary section through the edge of the grinding wheel illustrating the positions of the grinding wheel and a drill being ground.

FIG. 15 is a plan view of the end of a twist drill.

FIG. 16 is a fragmentary side elevation at one end of the drill when viewed in the direction of the arrow 16 in FIG. 15.

FIG. 16a is a view similar to FIG. 16 of the drill viewed in the direction of arrow 16a in FIG. 15.

'FIG. 17 is a schematic of the electrical circuit of the control system.

FIG. 17a is a legend for FIG. 17.

FIG. 18 is a schematic of the air and hydraulic control system.

DESCRIPTION OF A PREFERRED EMBODIMENT General Referring now to the drawing, there is shown therein apparatus for grinding twist drills constructed according to the present invention and which comprises generally a frame, referred to herein at X, which is shown only in fragmentary form since the precise construction of the frame is subject to a wide range of designs limited only by the requirement that it provide adequate support for the other components of the apparatus. The device also comprises a drill holder, indicated generally at H in FIG. 2, and shown in greater detail in FIGS. 8 and 9. As will be described in greater detail, the function of the drill holder is to receive, orient, and hold the drill firmly during the grinding operation.

The grinding 'wheel assembly is indicated generally at W in FIG. 1, the grinding wheel and its mount being shown in greater detail in FIGS. 2, 3 and 7. The wheel assembly W includes not only means for rotatably mounting the wheel but also movably mounting the wheel on frame X whereby the wheel is able to traverse a predetermined path along which it contacts the drill.

The wheel dresser is indicated generally at WD in 'FIG. 1 and is shown in greater detail in FIGS. 2 and 2a. This comprises means for restoring to a predetermined shape the surfaces of the grinding wheel after they become worn from use.

The operating and control system is shown in schematic form in FIGS. 17 and 18. An electro-mechanical control system comprising a plurality of air and hydraulic cylinders or motors, electric motors and control solenoids and relays constitutes a preferred embodiment of such operating and control mechanisms; but it is illustrated only as exemplary of such means and without any intention to be limitative on other features of the present invention.

Drill holder Drill holder H is shown in detail in FIG. 9 where it is seen that twist drill 10 passes through. collet 11 which can be contracted to grip and chuck the drill within the holder, and then through drill bushing 13 which centers the drill. Collet 11 has a plurality of fingers separated by longitudinally extending slots which have an external inclined surface at 12. Mounted externally of the collet and engaging inclined surfaces 12 is an annular cam 14 which is rigidly connected to a longitudinally movable piston 15 within a differential bore 16. Cam members 14 have inclined surfaces engaging the peripheral surfaces 12 on the collet so that axial movement of cam 14 compresses the fingers of the collet to grip drill 10.

This longitudinal movement of the cam is effected by piston 15 which has an annular surface at 15a in a radial plane. This surface is normally in engagement with an opposition radial surface 18 on a cup shaped receiver or cylinder 19. When air under pressure is introduced into the drill holder by a supply line 20, the air flows through passages 21 and 22 to cause shoulders 15a and 18 to separate. Piston 15 moves downwardly in FIG. 9 away from shoulder 18 on the cylinder, thus moving cam 14 in the same direction with respect to collet 11. The collet is held against movement in this direction by engagement with stop 23.

The movement of piston 15 downwardly in FIG. 9 compresses springs 24 which bear against the end of piston 15 and also against a fixed abutment ring 25 which is held in place by ring 26 threadedly engaging casing 33. When the air pressure is released, springs 24 cause piston 15 to return to the position shown in FIG. 9, thus releasing the collet and freeing drill 10. Flow of air through line 20 is controlled by a solenoid operated valve 29.

The drill holder includes means to rotate the drill 180 at the proper time during the grinding cycle. This rotation of the drill is accomplished by mounting ring gear 27 around cylinder 19, the gear teeth around the periphery of the gear engaging drive gear 28, as shown in FIG. 10, which is driven by the output shaft of reversible motor 30.

As may be seen in FIG. 11, the work holder includes stationary stop 31 which is arcuate in shape and is secured by screws 32 to casing 33 enclosing the work holder. Typically, stop 31 has its end faces spaced 90 apart around the axis of drill 10. Secured to ring gear 27 by bolts 34 is movable stop 35 which is in the same radial plane as fixed stop 31 so that its opposite end faces are adapted to engage the end faces of stop 31 to limit rotational movement of the assembly comprising cylinder 19, piston 15, cam 14, collet 11 and drill 10 held therein.

At one end of the range of travel by the drill motor, stop 35 engages one end of stop 31 as shown in solid lines in FIG. 11. Upon actuation of air motor 30, the other end of movable stop 31 is brought into contact with stop 35 which then occupies the dotted line position in FIG. 11, the relationship of the parts now being such that rotation of drill 10 through 180 is effected. Air motor 30 is reversible so that upon being actuated a second time, the cylinder and the drill are rotated back to their initial starting position. Air under pressure for this purpose is supplied to motor 30 through supply lines 37, flow of air being regulated by a solenoid operated reversing valve 38.

In addition to firmly holding drill 10 during the grinding operation, a chief purpose of the drill holder is to orient the drill properly with respect to the grinding wheel. The axis of the drill is, of course, established by collet 11 when the drill is chucked in the holder. However, it is also necessary to orient the drill both longitudinally and angularly with respect to the drill axis. Po- I sitioning of this latter nature is accomplished by drill locator 40. Locator comprises head 41 which has an integral threaded stem 42 in an opening in U-shaped arm 43. Lock nut 44 on stem 42 can be tightened against the arm to lock head 41 in any adjustable rotational position. Arm 43 is pivotally mounted by shaft 45 on the end of drill holder housing 33.

In the full line position of FIG. 10, the locator arm holds locator head 41 in position to be engaged by drill 10 as shown in FIG. 9. However, as will become apparent, it is necessary that the locator be swung away from this position in order for the grinding wheel to reach the end of the drill; and this movement of the locator is accomplished by piston 48 in cylinder 49 which is formed by a bore in holder casing 33. The outer end of piston 48 is connected by a pin and link 50 to shaft 45 by which the locator arm is pivotally mounted on casing 33.

Supply line 51 provides compressed air to the inner end of cylinder 49, the air therein driving the piston 48 outwardly to move arm 43 to the broken line position 43b in FIG. in which locator head 41 is moved away from contact with the end of drill 10.

The face of locator head 41 is shown in detail in FIG. 9a. The face of the head is flat and establishes a plane which, by engaging the extreme tip of drill 10, orients the drill longitudinally of the drill axis. Mounted on the face to project outwardly therefrom is an abutment or blade 41a so positioned that it engages the leading edge of one of the two primary cutting edges of the twist drill. This is accomplished in the machine by rotating drill about its longitudinal axis until one of the cutting edges engages face 41b of abutment 41a. This motion orients the drill angularly about its longitudinal axis.

In operation of the machine, these two motions of the drill are accomplished manually by the operator. When the machine is then placed in operation, collet 11 is first closed to engage the drill, thus firmly holding it and orienting the drill to establish the proper position of the longitudinal axis of the drill, after which air is introduced through line 51 to raise piston 48 and swing arm 43 to the broken line position of FIG. 10 in which the locator is removed from contact with the drill.

Although the drill holder is stationary while the grinding wheel is in contact with the drill, the drill holder is mounted adjustably upon frame X in order to effect a precise location of the drill with respect to the grinding wheel. The means for mounting the drill holder on frame X are shown in FIGS. 3 and 8. The drill holder is supported on an angular mounting bracket 55, the base of which is attached by screw 56 to post 57. The bottom end of the post is pivotally mounted by pin 58 to a short link 59 which is likewise pin connected at its other end at 60 to a portion of frame X.

The centers of the two pins 58 and 60 are at substantially the same level so that link 59 extends horizontally. The link has a downwardly projecting shoulder 61 which is engaged by horizontally extending adjustment screw 62 that is threaded into frame X. It is preferably provided with a. calibrated head which cooperates with an index on the frame so that the position and movement of the screw can be accurately observed and controlled. It will be seen that inward movement of screw 62, when viewed as in FIG. 3, moves shoulder 61 clockwise around pivot 60, thereby raising pin 58 and shifting post 57 vertically upward. The reverse movement of screw 62 lowers post 57 so that the post and drill holder H carried thereby can be adjusted vertically as indicated by arrow 63.

Post 57 is held in its substantially vertical position by one or more springs 65 which are connected at one end to the post and at the other end to frame X. Being in tension, these springs pull the post clockwise in FIG. 3 against a second adjusting screw 66 which, like screw 62, is threaded into frame X and is provided with a calibrated head which in cooperation with an index on the frame permits the position and movement of the screw to be accurately controlled and determined. Turning adjusting screw 66 in one direction moves it inwardly against post 57, causing the post to rock counterclockwise about pivot 58; while the reverse rotation of screw 66 allows the post to be moved clockwise about pin 58 in response to the pull of springs 65. This effects horizontal adjustment of the location of the drill holder as indicated by arrow 67.

While the horizontal and vertical adjustments of the drill holder are, strictly speaking, over arcuate paths because of the pin connections at 58 and 60, it will be realized that for practical purposes each movement may be considered as linear. This is true because the normal range of movement is only a few thousandths of an inch, or perhaps a few hundredths of an inch at most, and the departure of an arc from a straight line under these conditions is negligible.

In addition to the horizontal and vertical movements just described, which may be considered as linear adjustments, the drill holder is provided with two bodily angular adjustments, one about a vertical axis and one about a horizontal axis. The adjustment about the vertical axis can be effected by loosening machine screw 56 and rotating the drill holder and its mounting bracket 55 about the vertical axis established by machine screw 56. When the proper position is obtained, the screw is again tightened to hold the drill holder in place. A circular scale may be provided as shown in FIG. 8a to measure rotational movement.

The other adjustment is accomplished by changing the position of the holder casing with respect to mounting bracket 55. This is accomplished as shown in FIG. 8. The upwardly extending flange of mounting bracket 55 is provided with a pair of arcuate slots 55a through which pass adjusting screws 68, as shown in FIG. 1. By loosening screws 68, the motor can be tilted angularly in a vertical plane established by the upwardly extending flange of bracket 55, after which the screws are tightened to lock the drill holder in place.

Grinding wheel assembly and swing arm Referring now to FIGS. 1, 2, 3, 7 and 13, the grinding wheel assembly W is seen to include grinding wheel 70 which is mounted to rotate about a vertical axis and is movably mounted on frame X. The grinding wheel has one peripheral face 71 which is of frusto-conical shape and is the principal grinding surface. It also has a second frusto-conical surface 72, the two surfaces meeting at the maximum diameter of the wheel which is in a horizontal plane at substantially the center of the wheel.

Wheel 70 is secured to spindle 73 in any suitable manner, as by clamping the wheel between a pair of washers 74 which are nonrotatably connected to the spindle. Spindle 73 is rotatably mounted in journal bearing 75 to rotate about a vertical axis, the spindle projecting below the journal bearing to carry on its lower end a driven pulley 76, as may be seen in FIG. 7. Drive belt 77 passes around pulley 76 and also around drive pulley 78 on the output shaft of electric motor 80.

By reference to FIG. 2, it will be seen that the base of motor 80 is mounted on pad 81 on the end of arm 82 which in turn is pivotally mounted at 8211 on the slide 86 described immediately below.

Extending from front to rear at the top of frame X is a major bridge-like support member 83 (FIG. 3) which serves as a foundation for the grinding wheel assembly. Upon this foundation member is supported pivot 84 by which swing arm 85 is mounted. Swing arm 85 is angular and is pivoted at one end at 84. Upon it is mounted slide 86 to which are connected motor arm 82 and spindle bearing 75.

Journal 75 for the grinding wheel spindle is slidably mounted on arm 85, as by slide 86 and the dovetail mounting 85a seen in FIG. 7. This dovetail 8511 enables the grinding wheel and its drive motor to move horizontally along the swing arm and radially of its swing in order (a) to move the grinding wheel away from the drill after the grinding cycle is complete to give clearance for the locator, and (b) to move the grinding wheel away from the dresser tools for return stroke clearance.

Swinging movement of arm 85 is effected by hydraulic cylinder 88, seen particularly in FIGS. 3 and 13. One end of cylinder is pin connected at 89 to a stationary mounting bracket attached to frame member 83. The piston rod 90 projecting from the other end of cylinder 88 is pin connected at 91 to a short bracket 92 (FIG. 2b) extending laterally from the swing arm. Thus as hydraulic pressure in cylinder 88 draws piston rod 90 into the cylinder, the swing arm moves counterclockwise about pivot 84 to the dotted line position viewed as in FIG. 13. When the hydraulic force is reversed and the piston rod is extended from the cylinder, the swing arm is then moved back clockwise, the end of this movement being the standby position shown in FIG. 2.

As mentioned above, the grinding wheel and its motor are both mounted on side 86 which in turn is mounted on dovetail 85a carried by the swing arm. The dovetail provides a horizontal way along which the grinding wheel is moved back and forth horizontally under the action of hydraulic cylinder 94. One end of the cylinder is pin connected at 95 to bracket 96 mounted on one side of arm 85 (FIG. 7). The piston rod 97 projecting from the other end of the cylinder is pin connected at 98 to lever 99 which, as shown in FIGS and 6 is pivotally connected by a pair of pins 100 to swing arm 85. The two pins establish a vertical axis about which lever 99 is rocked by rod 97.

Lever 99 carries a pair of pins 101 which engage opposite sides of sleeve 102 at an annular groove on the exterior of sleeve 102, as shown in FIG. 4. Sleeve 102 is slidably mounted and guided by passing through a bore in swing arm 85, while the interior of the sleeve is threaded to engage mating threads upon adjusting screw 103 which is within sleeve 102 and extends beyond the sleeve at each end thereof. One end of screw 103 is anchored to slide 86 by a set screw 104 in boss 105 into which the end of screw 103 extends. Boss 105 is a part of the slide on which the grinding wheel and its drive motor are mounted. The purpose and adjusting function of screw 103 will be explained later in connection with the wheel dressed assembly WD.

At the other end of this adjusting screw assembly, sleeve 102 has an extension 102a which carries the sleeve outwardly at the rear of the machine beyond the frame and cover plates, as shown clearly in FIG. 4. On the end of this extension is mounted hand wheel 106 by means of which the sleeve can be rotated relative to its adjusting screw 103. Inside sleeve extension 102a is an extension 103a of the adjusting screw. The extension is longitudinally slotted at 107 and a transversely extending pin 108 passing through the stem of screw 103 is longitudinally movable in slot 107 with respect to extension 103a; but the pin establishes a non-rotatable connection between the stem of the adjusting screw and the extension 103a.

Beyond hand wheel 106 is lock screw 110 which is a thumb nut threaded onto screw 111 secured to the end of extension 103a. When thumb nut 110 is tightened, the sleeve 102 and its extension are locked to screw 103 and its extension so that they do not rotate with respect to each other but are capable of longitudinal movement in unison. When the thumb nut is released, relative rotation between the two members is accomplished by rotating hand wheel 106 the effect of which is to move the sleeve relative to the screw and thereby to change the length of the adjusting screw assembly.

The sleeve and adjusting screw assembly illustrated in FIG. 4 has a dual function. In the first place, it acts as a rigid member attached to boss 105 to advance and retract slide 86 and the grinding wheel along the swing arm. In the second place it serves as a member of adjustable length to relocate the grinding wheel as it becomes worn, with respect to the dressing tools later described and also relative to a drill in holder H.

For the latter function, the overall length of the sleeve and screw can be varied by turning hand wheel 106 and the attached sleeve 102 to advance or retract the adjusting screw which is connected by screw threads to the sleeve. Assuming that boss 105 is shown in a position occupied when grinding wheel 70 is of full diameter, the boss is gradually moved to the right in FIG. 4 to compensate for reduction in diameter of the grinding wheel occurring due to wear or other causes.

When the sleeve and adjusting screw are locked by thumb screw 110 the assembly becomes a rigid member which is advanced and retracted by movement of lever 99 which engages the assembly at pins 101. Thus it will be seen that regardless of the spacing between pins 101 and boss 105 which is introduced to compensate for reduction 8 of grinding wheel diameter, the actual advance of the wheel is controlled entirely by movement of lever 99 and is uniform independently of the wheel diameter.

To actuate the elements of the control system later described, various limit switches are provided in positions to be operated by movement of swing arm 85. In FIGS. 2 and 212 there is shown limit switch LS1 which is a double throw switch operated by a pair of arms 160 and 161. In the position of FIG. 2b, arm 161 projects into the path of extension 162 of bracket 92. During the advance stroke of the swing arm, switch arm 161 is engaged by extension 162 and the two switch arms are rotated to the alternate broken line position of FIG. 2b. Near the end of the return stroke of swing arm the same extension 162 engages switch arm 160 and returns both arms to the full line position.

Two limit switches LS3 and LS4 are shown in FIG. 2. They are mounted one at each of two opposite sides of an upright portion of the foundation member 83. These switches are engaged by adjustable members 165 and 166 respectively mounted on the swing arm. The functions controlled by these switches will be described later in connection with the operating circuit.

Wheel dresser assembly When grinding wheel 70 becomes worn, it is necessary to dress the wheel in order to restore the grinding faces 71 and 72 to their proper shapes. This is accomplished by the dresser assembly WD which is seen particularly in FIGS. 2 and 2a. The dresser assembly comprises a base which supports the dresser of the operating cylinders.

Each follower 132 and 133 is pressed against its associated cam face by suitable pressure applying means. Such means preferably includes a pair of air cylinders and pistons 137, one for each arm 121 and 122 shown diagrammatically only in FIG. 18, which act as air springs. The cylinders can be energized or de-energized as required, as described below to hold the dressing tools firmly in a predetermined path or to release them for free movement.

'It will be noticed that the wheel dresser assembly WD is so located with respect to swing arm 85 that sliding movement of wheel 70 along the arm brings the grinding wheel toward dresser tools 123 to the dotted line position of FIG. 2a. This is accomplished by activating hydraulic cylinder 94 which moves slide 86 along dovetail ways 85a. Swing arm 85 being at the extreme range of movement away from the drill and holder H, the outward linear movement of the grinding wheel is only that indicated 140 in FIG. 13, the grinding wheel moving from the dot-dash position 70a to the full line position 70b at which it is adjacent but just beyond the dressing tools 123. Now movement of the dressing tools guided by contact with cam causes the tools to traverse the grinding surfaces on wheel 70 to dress the grinding surfaces to the desired shape. In order to maintain the grinding wheel at the dressing tools during the dressing operation, arm 85 is held by cylinder 88 against movement at this time.

The wheel dresser assembly WD is located on the arc of the swing arm travel and with relation to the drill holder so as to make it self-compensating, that is, although the grinding wheel is adjusted toward the diamond to re-dress the wheel, after the wheel is dressed it is in the same relative position to the drill holder as it was before dressing. At the dressing position of the arm, the dressing tools are on a line passing through the center of pivot 84 and the axis of rotation of wheel 70, which line is a radius of the arc traversed by a point on the edge of the wheel. The compensating or correcting movement of the wheel produced by turning hand wheel 106 and adjusting screw 103 is along this radius, with the result that said point on the extreme edge of the wheel at this radius always traverses the same arcuate path as the arm swings, regardless of the diameter of the grinding wheel. Thus the point on the grinding wheel contacting the drill continues to move in a predetermined path with respect to the drill. This relation insures precision grinding as the wheel is re-dressed and corrects or compensates for the reduction in wheel diameter caused by dressing.

Grinding drills One conventional grinding technique for a drill produces a conical surface on the working end. Viewing the end of a drill as in FIG. 15, this produces a cutting edge 141 along the leading edge of each flute while behind each of the flutes is a conical surface, indicated at 142. The two conical surfaces meet at the center of the drill along a short, straight line which provides a chisel point at which little or no cutting takes place. It is a purpose of the present invention to grind drills with a high degree of precision in such a manner that this chisel point is eliminated and instead secondary cutting surfaces are provided. Such grinding produces what is commonly referred to as a split point, the operation being referred to as splitting the drill. It consists of removing material from the heel of each flute at surface 142 to produce a surface at 143 on each flute which is at an angle with respect to the conical surfaces 142. The result is a secondary cutting edge 144 along the line which was formerly the intersection of two conical surfaces. This secondary cutting edge 144 is produced because removal of material from surface 142 to form surface 143 extends inwardly to the center of the drill, dropping the ground surface 143 with respect to conical surface 142 on the other flute. Two of these secondary cutting edges 144 are formed facing in opposite directions.

This material is removed from the heel of the drill by grinding surface 71 with the drill in the position with relation to the grinding wheel as shown in FIG. 14. The angle that face 143 makes with the axis of the drill is commonly referred to as the notch angle and is that angle indicated at 146 in FIG. 16a.

The radial line of intersection between surfaces 142 and 143 on one flute may not pass directly through the axis of the drill in which case they are slightly oifset from one another as shown in FIG. 15. This total amount of offset is spoken of as the web thickness and is indicated at 147 in FIG. 15. By careful adjustment, this distance may be reduced to substantially zero. It will be seen that when grinding a surface 143 the plane of maximum diameter of wheel 70* is substantially at the longitudinal axis of the drill, Since it is of paramount importance for accurate drilling that the flutes be ground exactly the same, the drill holder is designed to rotate the drill 180 as closely as possible so that the two flutes are ground equally and in succession, the ground surfaces thus being accurately symmetrical about the drill axis and not being influenced in any way by any eccentricity in the flutes themselves.

It is in order to provide the desired degree of accuracy in grinding the drill that various adjustments, as described before, have been provided for the drill holder H. Thus the vertical and horizontal movements produced by controls 62 and 66 respectively affect the relative position of the secondary cutting edges and the web thickness. The drill is located in the holder in such a position that the horizontal control moves the grinding wheel in a direction to move the secondary cutting edges 144 closer together or farther apart. The web thickness at 147 can be controlled by movements of the vertical control 62. These two controls in combination give the operator a close control over the final shape of the drill point.

The notch angle is regulated by the setting of the drill holder H about the vertical axis of screw 56. Accordingly, the notch angle is varied by the angular setting of the drill holder about the'vertical axis. The secondary cutting edges 144 are preferably undercut slightly with 10 respect to the axis of the drill, that is, they do not lie precisely in planes containing the drill axis. This departure from a truly longitudinal plane is termed the rake angle and its size is controlled by the angular position of the drill holder about a horizontal axis. It can be adjusted by loosening the screws 68 to secure the desired adjustment of the drill holder.

Another adjustment is also possible which changes the shape of the drill point and that is the angular rotation of the drill about its longitudinal axis with respect to the grinding wheel. This is effected by changing the position of blade 41a on locator head 41 by rotating the locator head about its mounting on arm 43. To do this, lock nut 44 is first loosened and the stem 42 is then rotated to the desired position and nut 44 is tightened. Since the drill is oriented by engagement of one of the primary cutting edges 141 with the locator blade, a change in the position of the blade eifects a change in the secondary cutting angle, that is the angle 148 between a primary cutting edge and a secondary cutting edge on the drill.

Control circuits For obvious reasons it is desirable that various motor means be provided to supply power for carrying on the movements and operations of the machine. One such motor means is electric motor driving the spindle carrying grinding wheel 70. Another motor specifically mentioned above is the indexing air motor 30 on the drill holder. In addition, the several piston and cylinder arrangements, as at 88 and 94, are also motor means.

To operate these motor means, it is preferred but not necessary since other means may be employed, to provide a combined air and hydraulic system which is controlled electrically and is shown schematically in FIG. 18. This air-hydraulic system includes a number of valves which are operated by electrical solenoids. It is obviously desirable to provide an electrical circuit integrated with the air-hydraulic system which enables the various functions or operations of the machine to be carried out in the proper sequence or timed relation to other operations. For this purpose a typical electrical control circuit is shown schematically in FIG. 17. Like the air-hydraulic system, it will be realized that the electrical circuit is merely one circuit which will accomplish the desire-d automatic operation of the drill splitter and that other electrical circuits may be employed to perform the several functions of the machine in the same or different sequences. Also, various additions may be made to either the air-hydraulic system or to the electrical circuit, as may be desired.

Operation Having described the principal components of the drill grinder, its operation will now be described with reference to FIGS. 17 and 18.

The complete cycle of operations can best be understood by considering in succession the several stages of operation. Thus initially a starting switch S2 on the front panel (FIG. 1) is pressed to energize both the hydraulic and electrical circuits and place the machine in an operative but standby condition. After this the grind cycle is initiated by the operator pressing a second closing switch S3 causing the machine to automatically go through the grinding cycle after which the machine again comes to a stop in the standby condition. The cycle of dressing the wheel may be automatically carried out after the grinding cycle but for purposes of disclosure here will be considered as being initiated manually by the operator, allowing separate control of this operation.

Referring now to FIG. 17, it will be seen that power is supplied to the machine over conductors 201 which preferably pass through switch S1 which is the access panel interlock switch, a protective measure which is well known. Conductors 201 pass through the contacts operated by motor contactor MC to the main motor 80 which drives the grinding wheel. Power for the control circuit is 1 1 taken from one pair of conductors 201 through a step down transformer T. From the secondary of the transformer T are a pair of leads 202 and 203 which supply power to all of the several solenoids, relays, and other components of the electric circuit.

When start switch S2 is pressed, the electrical circuit and the air-hydraulic system are placed in the standby condition as follows:

(1) Motor contactor MC is energized, thus closing the relay contacts to motor M, which now starts and drives the grinding wheel.

(2) Solenoid B is energized through contact 210 of control relay R3. Solenoid B controls the standby position valve for swing arm 85. The circuit to solenoid B is also completed through normally closed contacts 205 and 204 of a switch which is actuated by clutch coil 212 of the stroke counter mechanism. The stroke counter is an optional feature incorporated into the electrical circuit to cause the wheel to traverse its normal path with relation to the drill one or more times for each flute of the drill, as may be desired. Without such mechanism a single traverse, comprising a forward stroke and a return stroke, would be the normal operation of the machine; but introduction of the counter mechanism provides additional flexibility in operation.

(3) Index control relay R1 is energized through contact 214 of limit switch LS1.

(4) Contact 216 of control relay R1 closes and energizes the index control relay R4 through the serially connected contact 217 of index control relay R2. Relay R4 is now mechanically latched in the energized condition.

(5) Contact 222 of relay R4 closes and energizes solenoid D which controls the indexing valve 38 in the airhydraulic system.

(6) Solenoid D then places the indexing valve 38 in a first position which applies air pressure to one side of the indexing air motor of 30. This air pressure holds the air motor firmly in position, which may be assumed to be the starting position of the air motor, to keep the chuck in one extreme position at the time the drill is inserted therein. This condition insures proper drill orientation.

(7) Solenoid E is energized through contact 228 of the locator control relay R5. Solenoid E operates to close the locator valve which thus shuts 01f air to the locator cylinder, allowing arm 43 to drop the locator head opposite collet 11 in position for orienting drill 10.

(8) Motor contactor MC includes a latching contact connected across starting switch S2 which holds the circuit energized after the starting switch is released so that the starting switch is only momentarily depressed in order to energize the control circuits and place them in the standby condition described above.

With the control circuits energized, collet 11 is now open and ready to receive drill 10. The drill is inserted manually in the collet. Assuming that the work holder H has already been properly positioned by the various adjustments previously described, the next operation required on the part of the operator is to advance the drill into contact with the locator head 41 and rotate the drill lightly to bring one of the primary cutting edges into contact with blade 41a. Contact with the locator head thus orients the drill both lengthwise and angularly about its longitudinal axis with respect to the grinding wheel. The actual grinding cycle can now be started and this is initiated by the operator pressing cycle start switch S3. During the grinding cycle the electrical circuits and the air-hydraulic systems function as follows:

(1) Power is supplied to cycle start switch S3 through contact 210 of the dresser control relay R3 when relay is in the de-energized condition.

(2) When the cycle start switch S3 is pressed, it momentarily energizes the cycle delay relay DR in series with reset coil RC of the stroke counter mechanism.

(3) Cycle start switch S3 also supplies power through contact 211 of the chucking valve relay R6 to the chuck- 12 ing valve solenoid F. This energizes solenoid F which in turn energizes the chucking valve and the chucking cylinder 16. The chucking cyclinder 16 and piston 15 close the collet on the drill and hold the drill firmly in the grinding position.

(4) After a short delay, typically about two seconds, contact 232 of the cycle delay relay DR closes and momentarily energizes the reset coil RC of the stroke counter mechanism. As a result, an arm associated with reset coil 'RC mechanically actuates a clutch associated with stroke counter clutch coil CCC, causing the counter clutch to change position.

(5) When the counter clutch CCC changes position, it shifts switches S6 and S7 from the position shown in FIG. 7 to the alternate position and thereby energizes the chucking valve relay R6, locator relay R5, the infeed valve solenoid C through contact 213, and the swing arm valve solenoid A through contact 215. The change also deenergizes the swing arm standby position valve solenoid B by opening contacts 204 and 205.

(6) When the second valve relay R6 is energized, contact 227 closes and contact 211 opens. Chucking valve solenoid F remains energized.

(7) When the locator valve control relay R5 is energized, contact 228 opens and de-energizes the locator cylinder valve solenoid E. The locator valve then closes and actuates the locator cylinder, the cylinder then acting to swing the locator away from the drill point, thereby exposing the drill point to the grinding wheel.

(8) When the infeed valve solenoid C is energized by the counter clutch CCC, the infeed valve opens and actuates the infeed cylinder 94. The infeed cylinder then moves the grinding wheel towards the drill.

(9) When the standby position valve solenoid B is deenergized by the counter clutch, the standby position valve opens and removes the retract pressure from the swing arm cylinder which has been holding the swing arm at the extreme range of its movement in the starting position.

(10) When the swing valve solenoid A is energized by the counter clutch, the swing valve is opened by the solenoid. The swing valve opens and applies air pressure to the forward air-hydraulic cylinder which applies hy draulic pressure to the swing arm cylinder 88. The swing arm cylinder then starts the grinding wheel on its traverse path to the drill point. The forward and retract air-hydraulic cylinder shown in schematic form in FIG. 18 are merely conversion units in the system to enable the system to operate with full air and hydraulic fluids at different points. In a fully hydraulic system, it will be realized that these two conversion cylinders would be omitted and fluid could be supplied directly only to cylinder 88.

When the swing arm reaches the end of travel during the first grind cycle, it closes contact 207 of the limit switch LS1 and opens contact 206 of the limit switch LS1. The Wheel return limit switch LS4 is also closed.

1) Limit switch LS4 energizes the swing control relay R8. Contact 226 of relay R8 latches the relay in the energized position. Contract 229 of relay R8 de-energizes the swing valve solenoid A. This action removes air pressure from the forward air-hydraulic cylinder and applies air pressure to the retract air-hydraulic cylinder. This action applies hydraulic pressure to the retract side of the swing cylinder 88. The swing cylinder then moves the swing arm back to the start position. During the return stroke it again passes drill 10; and at the end of the return stroke a complete traverse of its path is accomplished. This is the end of the first phase of the grind cycle. However, if the counter mechanism is set to cause the grinding wheel to traverse its path again then additional forward and return strokes of the wheel are accomplished, following the same sequence of operations as just described.

(2) Contact 207 of the limit switch LS1 energizes the index relay R2 and pulses the counter clutch coil.

(3) Contact 206 of the limit switch LS1 opens and de-energizes the index relay R1. When relay R1 is deenergized, it removes the energizing power from the coil of the master index control relay R4, but relay R4 remains mechanically latched in the energized position to complete the circuit through it.

When swing arm 85 is returned to the starting position, the swing arm engages and closes contact 206 of limit switch LS1 and opens contact 207 of the same switch and establishes conditions for indexing the drill in the work holder. This index cycle is carried on as follows:

(1) Contact 206 closes, energizing index relay R1.

(2) When contact 207 of limit switch LS1 opens, the index relay R2 remains energized through contact 221 of relay R4 and contact 220 of relay R2.

(3) Contact 218 of relay R1 and contact 219 of relay R2, in series, energize the unlatching coil R4C for master index relay R4. This deenergizes relay R4 while relay R2 is held energized by contact 221 of relay R4.

(4) When relay R4 is de-energized, contact 222 of this relay opens and de-energizes the indexing valve relay solenoid D.

(5) Solenoid D then changes to position of the indexing valve 38 and the valve is now in position to apply air pressure to the opposite side of the work head indexing motor 30. Energizing work head motor 30 now causes it to rotate through 180, indexing the drill held in the drill holder in position to grind the second side or flute of the drill.

(6) When relay R1 is energized, contact 231 of R1 opens and de-energizes the swing control relay R8. Contact 229 of the swing control relay R8 then closes and energizes the swing valve solenoid A. This reverses the hydraulic pressure applied to swing arm cylinder 88, changing the pressure from the retract pressure to the forwardly acting pressure. Movement of the swing arm and the wheel in a forward direction initiates the second half of the grinding cycle that carries the grinding wheel past the drill after it has been indexed to 180 as de scribed.

Upon completion of the drill indexing cycle, the second grinding cycle begins immediately. The second grinding cycle is essentially the same as the first grinding cycle,

except that the master index control relay R4 remains de-energized so that the indexing valve solenoid D also remains de-energized. The indexing valve then holds the work head indexing motor 30 in the second position to grind the second flute on the drill.

At the end of the second forward stroke of the swing arm and the grinding wheel, the electrical circuit and the air-hydraulic systems function the same as previously described, initiating a second retract movement of arm 85 similar to the first retract movement of the swing arm and grinding wheel already described. The only ditrer-- ence is that the master index relay R4 remains in the de-energized position so that the indexing valve solenoid D also remains de-energized. This action holds the indexing valve in the second indexed position.

When contact 207 of limit switch LS1 opens at the end of the second retract stroke, this contact pulses the counter coil. This pulse causes the stroke counter clutch" to shift back to the start condition and all circuits are returned to the standby condition in which they are as described above.

Periodically, as may be required, the grinding wheel is dressed to restore it to its proper shape. This is accontact 210 of relay R3 which disables the cycle start circuit including switch S3 and de-energizes the swing standby position valve solenoid B. When solenoid B is de-energized, swing arm moves the grinding wheel to the dress positiOn.

(2) Contact 224 of relay R3 closes and supplies holding power through limit switch 182 to the coil of relay R3. At the same time, contact 213 of relay R3 energizes the infeed valve solenoid C.

(3) Energizing solenoid C closes the infeed valve and supplies air pressure from the infeed valve to cylinder 94 and to the dresser cam air springs 137. Pressure in cylinder 94 actuates the piston and starts the grinding wheel slide moving along the swing arm toward the dresser diamonds, the amount of movement being determined by the setting of dresser adjusting wheel 106.

(4) When the swing arm moves to the dress position, it closes limit switch LS3 whereby contact 225 of relay R3 supplies power through the limit switch to energize the dresser master cylinder valve solenoid G.

(5) Solenoid G opens the dresser master cylinder valve, which then applies air pressure to the dresser master cylinder 129a. The master cylinder applies oil pressure simultaneously to the top and bottom dresser diamond cylinders and 126. The pistons moving outwardly in each of these cylinders then move the top and bottom dresser arms toward the grinding wheel and diamonds 123 dress the wheel 70.

(6) Upon completion of the dress cycle stroke, the dresser master cylinder opens the limit switch LS2. Open ing this switch de-energizes the dresser control relay R3 and the electrical circuits. Now the air-hydraulic systems return to the standby condition with the grinding wheel remaining in the dress position until cycle start switch S3 is depressed to start a grinding cycle, as previously described.

All of the circuits are de-energized by opening stop switch S4 which being in series with start switch S2, interrupts the power supply to the motor controller and to all other electrical circuits, thereby opening the relay supplying power to motor '80 and bringing all motors to a stopped condition.

In FIG. 7 various valves V are shown in the fluid lines. These are throttling valves preferably manually adjustable to regulate the rate of fluid flow and consequently the rate of movement of the respective mechanical elements actuated thereby. It will be realized that various other elements may be added to either the electric circuit or the air-hydraulic system; for example, it may be desired to provide for recirculation of a coolant supplied to the drill during the grinding operation, as is well known practice in the art.

From the above it' will be understood that various changes in the apparatus and the control means therefor may occur to persons skilled in the art without departing from the spirit and scope of the present invention. A01 cordingly, the foregoing description is considered as being illustrative of, rather than limitative upon, invention as defined by the appended claims.

We claim:

1. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for non-rotatably holding a drill in a predetermined position during the grinding operation;

a rotatably mounted grinding wheel supported by the frame, said wheel having an outwardly facing frustoconical grinding surface;

means for rotating the grinding wheel; and

means causing the grinding wheel to traverse during a grinding operation an arcuate path lying in a plane perpendicular to the axis of rotation of the grinding wheel and along which path said frusto-conical face contacts the end of the drill, the grinding wheel be- 15 ing disposed between the center of the arcuate path and the drill.

2. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position;

a rotatably mounted grinding wheel supported by the frame, said grinding wheel having two peripheral surfaces of frusto-conical shape intersecting at the maximum diameter of the Wheel, said maximum diameter engaging the drill at substantially the axis of the drill whereby both frusto-conical surfaces of the grinding wheel are in grinding contact with the drill simultaneously;

means for rotating the grinding wheel; and

means causing the grinding wheel to traverse during a grinding operation an arcuate path along which it contacts the end of the drill, the grinding wheel being disposed between the center of the arcuate path and the drill.

3. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position, said drill holder including locator means engaged by the end of the drill to establish the position of the drill both longitudinally and angularly in the holder and with respect to the path of the wheel; and

fluid actuated collet means for gripping and holding during grinding a positioned drill;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel; and

means causing the grinding wheel to traverse during a grinding operation an arcuate path along which it contacts the end of the drill, the grinding wheel being disposed between the center of the arcuate path and the drill.

4. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position, including means rotating the drill 180 between two successive traverses of the grinding wheel;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel;

and means causing the grinding wheel to traverse a path along which the wheel contacts the end of the drill.

5. Apparatus for grinding the end of a twist drill, comprising:

a frame; a drill holder for holding a drill in a predetermined position;

means mounting the drill holder on the frame for adjusting movement of the drill holder about two intersecting and mutually perpendicular axes relative to the grinding wheel path;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel; and

means causing the grinding wheel to traverse during a grinding operation an arcuate path along which it contacts the end of the drill, the grinding wheel being disposed between the center of the arcuate path and the drill.

6. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for holding a' drill in a predetermined position;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel;

means causing the grinding wheel to traverse a path along which the wheel contacts the end of the drill; and

grinding wheel dresser means positioned to be engaged by the grinding wheel at a selected position in the normal range of traverse of the wheel along said path.

7. Apparatus for grinding the end of a twist drill comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position, the drill holder having locator means engaged by the end of the drill to establish the drill in a predetermined position both longitudinally and angularly in the drill holder and with respect to the path of the grinding wheel;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel; and

means causing the grinding wheel to traverse a path along which the wheel contacts the end of the drill, including a pivoted support for the grinding wheel and motor means moving the support and the grinding wheel back and forth over an arcuate path, the wheel having a frusto-conical surface brought thereby into contact with the drill.

8. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel;

means causing the grinding wheel to traverse a path along which the wheel contacts the end of the drill; and

cyclic operating mechanism comprising:

first motor means traversing the wheel forward and return over said path;

and second motor means rotating the drill in the holder between two successive complete traverses of the grinding wheel.

9. Apparatus according to claim 8 which also includes means deactivating the first motor means after two complete traverses of the grinding wheel.

10. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position;

a rotatably mounted grinding wheel;

means for rotating the grinding wheel;

pivoted support means for the grinding wheel and the last mentioned means for movement of the grinding wheel over an arcuate path with respect to the drill;

a first motor means traversing the grinding wheel and its pivoted support means over said path;

means slidably mounting the grinding wheel on the pivoted support means for linear movement on the pivoted support means;

and second motor means slidably moving the grinding wheel on the pivoted support in timed relation to the traversing movement of said first motor means.

11. Apparatus as in claim 10 in which the sliding movement of the grinding wheel on the pivoted support means is in a direction transverse to the arcuate path;

and second motor means is actuated at the initial end of the arcuate path.

a drill holder mounted on the frame for holding a drill in a predetermined position;

a rotatably mounted grinding wheel supported by the frame, the grinding wheel having two oppositely inclined frusto-conical surfaces;

means for rotating the grinding wheel;

means causing the grinding wheel to traverse a path along which the wheel contacts the end of the drill;

and wheel dresser means having two dressing elements that simultaneously scan the two frusto-conical surfaces on the wheel to dress said surfaces.

13. Apparatus for grinding the end of a twist drill,

comprising: i

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel; and

means causing the grinding wheel to traverse a path along which the wheel contacts the end of the drill;

the drill holder comprising:

a drill holding collet rotatably mounted in a casing;

fluid actuated piston means engaging the collect and movable under fluid pressure in a direction to close the collet against a drill therein;

spring means urging the piston to a normally open position; and

reversible fluid motor means operatively connected to the collet to rotate the collet alternately in opposite directions.

14. Apparatus according to claim 13 which also includes respective solenoid actuated valve means controlling fluid flow to each of said motor means and said piston means; and electric circuit means effecting sequential operation of the individual solenoid operated valve means in timed relation with each other.

15. Apparatus according to claim 10 that also includes wheel dresser means having a dressing element that engages the grinding surface on said grinding wheel when the grinding wheel is at one end of the range of linear movement.

16. Apparatus for grinding the end of a twist drill, comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel;

means, including an arm pivotally mounted on the frame and carrying the grinding wheel for movement over an arcute path causing the grinding wheel to 17 12. Apparatus for grinding the end of a twist drill, comprising:

a frame;

18 traverse a path along which the Wheel contacts the end of the drill;

grinding wheel dresser means;

and means adjustably positioning the grinding wheel along the arm radially of the arcuate path for engagement by said dresser means.

17. Apparatus for grinding the end of a twist drill,

comprising:

a frame;

a drill holder mounted on the frame for holding a drill in a predetermined position;

a rotatably mounted grinding wheel supported by the frame;

means for rotating the grinding wheel;

an arm pivotally mounted on the frame to swing over an are;

a slide mounted on the arm for linear movement relative thereto, said slide carrying the grinding wheel and the means for rotating the grinding wheel;

means to move the slide relative to the arm and including a member of variable length to adjustably position the wheel with respect to the slide and independently of the length of the linear travel of the slide and the wheel on the arm;

and meanus causing the grinding wheel to traverse a path along which the wheel contacts the end of the drill.

18. Apparatus according to claim 4 that also includes locator means engaged by the end of the drill to position the drill within the drill holder; and

fluid actuated means mounting the locator means on the drill holder for movement into and away from a drill-engaging position.

19. Apparatus according to claim 18 in which the drill holder includes fluid actuated collet means for gripping and holding a positioned drill for grinding operations and fluid actuated motor means for rotating the drill between traverses; and

the apparatus also includes a control system actuating the several fluid actuated means in timed sequence with each other. 20. Apparatus according to claim 13 that also includes drill locator means engaging the drill to orient the drill both longitudinally and angularly in the drill holder.

References Cited UNITED STATES PATENTS 3,117,396 1/1964 Dalton 51-33 1,162,304 11/1915 Neuens 51206 X 3,057,122 10/1962 Hewes et al 51125 3,178,857 4/1965 Grab et al 51-33 OTHELL M. SIMPSON, Primary Examiner US. Cl. X.R. 51-l24 

